Understanding the cellular and molecular mechanisms underlying the order and precision of compensatory liver regeneration is essential for understanding and intervention in liver carcinogenesis and toxicology as well as development of strategies for liver cell transplantation and gene therapy. Increasing evidence indicates that response to damage by the normal liver is orchestrated by activation and repression of the activity of multiple cytokines within the liver rather than external hormones. Dysfunction of this ordered process results in progression to malignancy. The FGF family of fourteen ligands, their tyrosine kinase receptors (FGF-R) (four genes, 16 splice variants resulting in greater than 100 isoforms) and their heparan sulfate proteoglycan co- receptors within liver are involved in the transient regulation of growth and function in both parenchymal and non-parenchymal cells and the dysfunction leading to hepatoma. This continuation project will characterize significance of expression of FHF-13 (FGF-13) in liver and hepatomas. FGF and FGFR specific heparan sulfate proteoglycan (HSPG) subunits of the FGFR signal transduction complex will be isolated from liver cells, characterized and cDNA coding for their protein cores will be identified by FGF and FGFR affinity chromatography. The promiscuity (or lack of it) of dimerization and functional interaction between FGFR isotypes will be determined in liver cells by using chimeric constructions of ectodomain with the TFG beta intracellular kinases. Impact of the four FGFR intracellular kinase domains and subdomains on mitogenesis, inhibition of cell growth and phenotype of liver cells will be determined using chimeric constructions of ectodomain and intracellular kinase domains. The role of the variant NH2-terminus of the major liver FGF polypeptide, FGF-1, and its proteolytic modification will be determined. Gene targeting to the liver in mice will be employed to dissect the functional role of FGFR1,2,3,4 and FGF-1, on resting and regenerating liver cell phenotypes as well as effect on development of hepatomas (collaborations with Dr. S. Thorgeirsson and Dr. J. Martin). From the results, the expression of FGFR 1,2,3,4 and their variants will be correlated with time and cell phenotypes in primary liver cell culture to mark rare transitional cell types related to mature hepatocytes and bile ductule cell lineages. A unifying hypothesis is presented on which the project is based in which specific FGFR and co-factor HSPG are associated with the mature phenotypes whereas transitional types are characterized by specific co-expression of FGFR and HSPG isoforms.